Modern efforts to reduce engine emissions and enhance engine performance have resulted in investigation into alternative engine combustion modes. Alternative combustion modes have been implemented for various types of engines.
For example for diesel engines, it has become apparent that conventional diesel combustion (heterogeneous charge compression ignition) can not alone meet the expected emission levels. The compression-ignition direct-injection (CIDI) engine is an advanced version of commonly known diesel engines, and is a promising technology for light-duty vehicles. It is suited to both conventional and hybrid electric power train configurations.
For diesel engines, alternative combustion modes include homogeneous charge compression ignition, low temperature combustion, and premixed charge compression ignition. Each of these alternate combustion modes has its own operating characteristics and requirements, such as emissions, speed-torque range, in-cylinder conditions, and fueling.
It further appears that combustion improvements alone may not be sufficient to meet emissions standards. More specifically, it may be necessary to use exhaust treatment devices in conjunction with combustion improvements. These treatment devices have their own operating characteristics, and some such devices require periodic regeneration.
To achieve emissions goals and satisfy engine requirements, the use of multiple combustion modes for the same engine is another concept being investigated. In particular, emissions treatment systems have operating requirements, such as gas composition and bed temperature, that must be satisfied over the speed-torque operating range of the engine. This can be accomplished by using different combustion modes for different operating conditions. For example, for a particular engine, a conventional combustion mode is used for starting and at higher loads, and a low-temperature combustion mode is used at light to moderate loads.